Wireless home automation systems for use in homes as well as in offices, shops, theaters or hospitals will be omnipresent in future for controlling a simultaneous and concerted performance of many devices. Such systems may for instance comprise lighting systems for controlling light sources and shadowing elements or sound systems for controlling loud speakers or other stereo-equipment.
A robust and reliable method for controlling such a system is based on unicast commands sent from a central controller to each individual device followed by an acknowledgment of the command sent from the respective device to the controller. This method may be suitable for controlling individual or few devices, e.g. for controlling the dimming of single lamps. Yet, for controlling the coordinated action of a device group, e.g. for applying a scene setup, unicast commands would fail to result in a simultaneous reaction of the respective target devices and would cause a visible delay and asynchronous responses (pop-corn effect).
Moreover, in low data rate networks, such as Zigbee or zwave, only a limited command rate is available. Certain commands may particularly load the network (for example those requiring high repetition rates or ones with high fan-out and/or fan-in) and cause network flooding, thereby provoking serious problems in controlling the system or inducing artifacts visible to a user. In particular, commands for dimming in a lighting system may easily overload the network.
As an alternative—less robust, but also less demanding with respect to the network capacity, the commands may be broadcast to the target devices. Yet, this holds the risk of a target device missing a command and thereby getting out of synchronisation with the other devices.
U.S. Pat. No. 5,010,459 A1 relates to a stage lighting system with a plurality of automated lamp units, wherein cue data for controlling the lighting effect are simultaneously broadcast to all lamp units during system initialization and stored in the individual lamp unit memories. Each lamp unit reacts individually to an updating command based on the stored data. However, if one lamp has missed an update, this will lead to visible disturbing artifacts in the scene illumination.
Particularly sensitive are commands for controlling a continuing synchronized action, which is performed by a multitude of devices for adjusting a continuously variable parameter of the devices, wherein the user stops the action, when a desired level is reached. For instance, a dimming action of a set of lamps can be controlled to adjust the illumination of a room and in particular when the initial and/or target end dimming levels are unequal (e.g. so-called scene dimming). When the desired level of brightness is reached, the user can stop the enduring dimming action. If a lamp in a lighting system has missed the broadcast stop command, it continues dimming beyond the desired level, although the other lamps have already stopped dimming.
Therefore, the question arises how to make broadcast or groupcast commands more robust and how to provide unobtrusive correctives to devices that have missed a command, without causing network flooding (e.g. by excessive network messaging caused by using high broadcast rates) or visible artifacts.